The long range purpose of the present project is to investigate the interaction of type-C viruses with lymphoid as well as fibroblastic cells, and to study the relationship between various tumor cell surface antigens and viral genome functions. The topics of current interest are: 1) The role of endogeneous type-C viruses in the etiology of reticulum cell neoplasms (RCN), particularly those of SJL/J strain of mouse which exhibit a high incidence of spontaneous RCN, and the use of this as a model for study of human Hodgkin's disease. 2) Virologic and immunologic characterization of tumors induced during the course of the above studies, especially a T-cell SJL/J lymphoma cell line (established in culture) and B-cell tumors of BALB/c as well as SJL/J origins classified as RCN. 3) Distinction between viral structural antigens and tumor specific transplantation antigens using nonproducer tumor cells originally transformed by type-C viruses.